Since the invention of integrated circuits, the semiconductor industry has experienced continuous rapid growth due to constant improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, these improvements in integration density have come from repeated reductions in minimum feature size, allowing more components to be integrated into a given chip area.
These integration improvements are essentially two-dimensional (2D) in nature, in that the volume occupied by the integrated components is essentially on the surface of the semiconductor wafer. Although dramatic improvements in lithography have resulted in considerable improvements in 2D integrated circuit formations, there are physical limitations to the density that can be achieved in two dimensions. One of these limitations is the minimum size needed to make these components. Also, when more devices are put into one chip, more complex designs are required. An additional limitation comes from the significant increase in the number and length of interconnections between devices as the number of devices increases. When the number and length of interconnections increases, both circuit RC delay and power consumption increase.
Three-dimensional integrated circuits (3DICs) were thus formed, wherein two dies may be stacked, with through-silicon vias (TSVs) formed in one of the dies to connect the other die to a package substrate. The TSVs are often formed in device dies after the front-end-of-line (FEOL) process, in which devices, such as transistors are formed, and possibly after the back-end-of-line (BEOL) process, in which the interconnect structures are formed. The formation of the TSVs may cause yield loss of the already-formed dies. Further, since the TSVs are formed in device dies after the formation of integrated circuits, the cycle time for manufacturing is also prolonged.